Fine root length production, mortality and standing root crop dynamics in an intensively managed sweetgum (Liquidambar styraciflua L.) coppice

Abstract

We used minirhizotrons and micro-video technology to study fine root production, mortality and standing root crop dynamics in an intensively managed sweetgum (Liquidambar styraciflua L.) coppice. The experiment was a split-plot design with two levels of fertilization. Low-level treatment plots received 560 kg ha-1 yr-1 fertilizer (19:9:19 NPK) via a drip irrigation system and high-level treatment plots received twice this amount. Approximately 150 cm yr-1 irrigation was applied to all treatments. There were no significant treatment differences in daily average fine root production or mortality. The phenology of fine root production and mortality, however, was characterized by strongly seasonal asynchrony. Production increased throughout the summer, peaked in September and declined sharply over the winter. Root mortality was not observed in either treatment until August, and then increased significantly throughout the winter months. There were also no significant treatment differences in standing fine root length. Standing live root length was greatest in the fall and dead root length was greatest over the winter. Roots in the upper 25 cm of the soil profile appeared to be significantly more dynamic (i.e. greater production and mortality) than deeper roots in both treatments. High levels of fertilization apparently do not alter fine root dynamics at our sites, in contrast to fertilization responses observed in other, more nutrient-poor environments.